Field of the Invention
The present invention relates to an FET (field effect transistor) with a source-substrate connection ("source-down FET") and a trench gate, including a drain zone of a first conductivity type provided on a first surface of a semiconductor layer of the first conductivity type which is disposed on a semiconductor substrate of the first conductivity type; the trench gate substantially penetrates the semiconductor layer; a source zone of the first conductivity type is provided at an end of the trench on a second surface of the semiconductor layer; and a semiconductor zone of the second conductivity type which is provided in a region next to the trench on the second surface of the semiconductor layer has a surface forming the second surface of the semiconductor layer together with the surface of the source zone. The invention also relates to a method for producing the FET.
FETs with a source-substrate connection have major advantages in terms of their cooling, because the cooling can be carried out by way of the silicon semiconductor substrate to which a voltage of 0 V is applied. It is thus possible, for instance, for an FET with a source-substrate connection to be screwed directly to the body of a vehicle, so that excellent heat dissipation is provided for.
U.S. Pat. No. 5,023,196 describes a MOSFET with a source-substrate connection and trench gate in which a first semiconductor layer of the second conductivity type and a second semiconductor layer of the first conductivity type are applied epitaxially over a semiconductor substrate of the first conductivity type, and a trench for the gate electrode is etched into those semiconductor layers down as far as the semiconductor substrate. The trench is lined with an insulating layer and is provided with a gate electrode. A source electrode is disposed on the surface of the semiconductor substrate opposite the trench, while a drain electrode is mounted in the region of the semiconductor layer of the first conductivity type, above a highly doped region of the first conductivity type.
Quite recently, so-called wafer bonding, in which two semiconductor wafers, one of which can be called a substrate, are joined together, has proved to be especially expedient for the production of semiconductor components and integrated circuits. If an FET with a source-substrate connection that is produced by wafer bonding is then desired, a construction of a connecting layer between the two wafers, and in particular a short circuit between the source zone provided in the lower region of the trench, and the semiconductor zone of the second conductivity type or so-called "body zone", is problematic.